The objectives of the proposed research are to increase understanding of host factors which interact with microbes and microbial factors to provide resistance to infectious diseases. The long term goals are to identify with precision, cellular and humoral components of the inflammatory response which bring about localization, killing and digestion of invading bacteria. The patient categories that will be studied includes neonates, patients with malignancy, patients with compromised immune status and patients with known susceptibility to recurrent bacterial disease. The cellular functions that will be studied include phagocytosis, intracellular killing, chemotactic responsiveness, migration, adhesiveness and reduction of nitroblue tetrazolium.